Reclaiming rubber



Patented Apr. 15, 1952 UNITED STATES PATENT OFFICE RECLAIMING RUBBERJoseph C. Elgin, Princeton, N. J assignor to U. S. Rubber ReclaimingCompany, Inc., Buffalo, N. Y., a corporation of New York No Drawing.

Application July 11, 1947,

Serial No. 760,501

my copending application Serial No. 618,573,

filed September 25, 1945.

The reclaiming of rubber from scrap material, such as old tires, shoes,mechanical goods, etc., i. e. the conversion of vulcanized rubber into aplastic mass which can be remolded and revulcanized into new'articles,is an old and well established industry. The purpose of the reclaimingprocedures is to soften or to plasticize the rubber sufficiently that,after adding various compounding and revulcanizing ingredients, it maybe remolded while leaving it in a chemical condition such that it can berevulcanized, e. g. in accordance with established manufacturingprocedures.

Various reclaiming agents have been used in such processes. Among theagents which have given effective results are various aliphatic andaromatic organic sulfur compounds, among them mercaptans, sulfides and,as disclosed and claimed in my copending application, disulfides. Amongsuch materials used by me and by others before the present invention areprimary aliphatic mercaptans, phenyl mercaptan (thicphenol), and primaryaliphatic sulfides.

Disulfides of this character, as set forth in my said application arespecifically and broadly claimed therein.

The primary compounds (i. e., those having but one other carbon atomvattached to the carbon atom which carries the sulfur) have beenconsidered best for this purpose, although certain secondary compoundshave also been employed. No tertiary mercaptans or disulfides had everbeen employed before this invention and there was no reason to expectthat they would have any outstanding utility for devulcanization, oreven equal the primary compounds.

I have now found that peculiarly effective results can be obtained inthe devulcanization of rubber and the like by the use of compoundswherein the sulfur bearing carbon (1. e., the carbon atom which isdirectly linked to a sulfur atom) is directly attached to three carbonatoms in addition to the sulfur atom. The present invention in itsbroader aspects contemplates the use of such materials generally, and incertain of its more specific aspects contemplates the use of suchmaterials wherein no sulfur atom has more than one carbon atom attachedthereto. Surprisingly effective results have been obtained, for example,by the use of tertiary mercaptans and tertiary disulfides in thereclaiming of rubber. These not only give more desirable reclaiming andbetter quality revulcanized materials, but are more active than theprimary compounds and most other available reclaiming agents. In someinstances the tertiary compound is more than twice as effective as thecorresponding primary compound.

The high molecular weight mercaptans such as tertiary dodecyl mercaptanand tertiary tetradecyl mercaptan and even higher have been effectivelyemployed and the lower mercaptans such as butyl mercaptan and those ofinter-.

mediate weight.

Similarly, with the disulfides one may use low:

molecular weight, especially di-tertiary-butyl disulfide, di-tertiaryhexyl disulfide, di-tertiaryoctyl disulfide, and higher molecularweight, such as di-tertiary-hexadecyl disulfide, and also tertiarydisulfides of intermediate weight.

The present invention increases the effectiveness and efficiency of theusual reclaiming processes and is also useful in certain improveddevulcanization procedures as, for example, those claimed in Patent No.2,415,449: of Edward F. Sverdrup and the present applicant.

In carrying out a procedure embodying the invention, the rubber, if notalready in a thin or finely divided form, is desirably sufficientlycomminuted either before or during the treatment so that the heat andreclaiming agents may penetrate it rapidly. It is advantageously groundin the usual manner into small particles.

The temperature of treatment should be above the boiling point of water,advantageously above about 300 F., and below the temperature of thermaldecomposition of the rubber. The most advantageous range is between 300and 450 F. The concentration of reclaiming agent in such case may beabout 0.1 %7% of the Weight of scrap rubber with distinct advantage inthe range 0.24%; and in special but infrequent cases may be profitablyas high as 15%. to be gained from a given increase of concentration ofthe reclaiming agent diminishes as the concentration increases and athigh concentrations may actually prove a disadvantage.

I Heating may be by any suitable means, e. g. radiant energy, especiallyinfra red radiation; alternating stresses, mechanical or electrical,especially high frequency alternating voltage, milling or mastication;or treatment on hot rolls or in heated mixing or extrusion apparatus;etc.

The advantage If undue vaporization of the reclaiming agent is to beavoided, it is advantageous to treat the mass of rubber in a confinedspace in which an appreciable vapor pressure of said agent ismaintained. For this reason an autoclave or extrusion plasticator, or anenclosed masticating or mixing mill, e. g. of the Banbury or Werner-Pfieider types, will be preferable to treatment in open air. A furtheradvantage of the confined treatment with volatile reclaiming agents isthat by reduction of pressure and sweeping with other gas or Vapor thereclaiming agent may be largely removed which aids in the termination ofthe treatment at the desired point. eral, excellent results have beenobtained by the use of screw plasticators of the type disclosed in thecopending application Serial No. 695,630, filed September 9, 1946.

Desirably, in certain instances, the mixture of rubber and reclaimingagent, with or without a softening agent, and/or other ingredients maybe treated in accordance with this invention in the form of a thin filmor other extended surface condition. Most advantageously, it is infinely divided crumbs making a porous mass into which the heatingmedium, e. g. saturated steam, can readily penetrate. r

The invention in its broader aspects is not only adapted for reclaimingvulcanized natural rubber but is also well adapted to the reclaiming ofsynthetic rubber, such, for example, as neoprene (a long-chain syntheticrubber made'by the polymerization of mono-chloro-butadiene), Buna S(GR-S, a copolymer of butadiene and styrene), Buna N (a copolymer ofbutadiene'and acrylonitrile), etc. The term rubber as used herein,except where otherwise qualified, is accordingly to be understood toinclude both natural and artificial rubber, especially the conjugateddiolefine polymers. In the specific examples, however,

-the names inner tube scrap, and tire tread scrap refer to naturalrubber scrap except where otherwise qualified.

Although I am giving below certain specific examples of my invention andits application in practical use and am giving also certainmodifications and alternatives, it should be understood that these arenot intended to be exhaustive or to be limiting of the invention. On thecontrary, I am giving these as illustrations and am giving explanationsherein in order to acquaint others skilled in the art with my inventionand the principles thereof and a suitable manner of its application inpractical use, so that others skilled in the art may beerlabled tomodify the invention and to adapt t and apply it in numerous forms, eachas may be best suited to the requirements of a particular use.

In the following examples the quantities of all ingredients are byweight unless otherwise specified. Natural rubber is treated except asspecifled.

Example I 380 parts of red inner tube scrap ground to In genmesh sizewere mixed with 4 parts of tertiary dodecyl mercaptan. The resultingmixture was heated-in pans in thin layers for 40 minutes at 338 F. inopen steam in an autoclave. The result was a notably satisfactoryreclaim of plasticity number 3.91. (Williams parallel plate 3 at 70 0.).

' Example [I 380 parts of red inner tube scrap ground to 30 mesh sizewere mixed with 20 parts of tertiary octyl mercaptan. The resultingmixture was heated in pans in thin layers for 40 minutes at 338 F. inopen steam in an autoclave. The resultwas a very soft reclaim ofplasticity number 1.83 (Williams parallel plate 3 at 70 0.).

Example III 380 parts of red inner tube scrap ground to 30 mesh sizewere mixed with 10 parts of tertiary butyl mercaptan. The resultingmixture was heated in pans in thin layers'for 40 minutes at 333 F. inopen steam in an autoclave. Theresult was a reclaim of good qualityPlasticity number 3.41 (Williams parallel plate).

Example IV 330 parts of red inner tub'e'scrap groundto 30 mesh size weremixed with 10 parts of tertiary octyl mercaptan. The resulting mixturewas heated in pans in open steam for six hours at 338 F. The resultingproduct was a reclaim of good quality. Plasticity number 5.36.

Escample V 380 parts of red inner tube scrap ground to 30 mesh size weremixed with 10 parts of tertiary tetradecyl mercaptan. The resultingmixture was heated in pans in open steam for six hours at 338 F. Theproduct was a reclaim of good quality. Plasticity number 5.47.

Example VI 100 parts of 2 mesh rubber tire tread scrap were mixed with1.5 parts of tertiary dodecyl mercaptan, 3 parts of process oil, 208parts of water, and 5 parts of caustic soda (76% soda ash). 5 hours at225 F. and 5 hours additional at 388 F. The resulting product afterbeing washed and dried gave a reclaim with properties equivalent tothose of a commercial alkali process re-- claim. The plasticity numberwas 4.9.

Example VII parts of red inner tube scrap were mixed with 0.50 parts oftertiary tetradec'yl mercaptan, 1.50 parts of Solvesso #3 (a higharomatic petroleum naphtha of boiling range 340-410 having a specificgravity of 0.883, an aniline point of Example VIII 47.5 parts of 24 meshtire peels and 47.5 parts 24 mesh Buna S tire peels were mixed with 1part tertiary lauryl mercaptan, 1.50 parts of Solvesso This was heatedin a closed digester for' #3, 0.5 part of water. This was processedthrough the plasticator at 14.4 pounds per hour, with a devulcanizingtime of approximately 9 minutes at about 400 F. The product was areclaim of good quality. Plasticity number 6.10.

Erample PX 380 parts of Buna S tire peels ground to 24 mesh size weremixed with 3 parts of tertiary lauryl mercaptan. 40 parts of petroleumresin (P. R. R. #1), 4 parts of lignin, and 2 parts of triethanol amine,and heated for 20 minutes at 338 F. in pans, in open steam. Theresulting product was a reclaim of good quality.

Example X 95 parts of natural rubber peels reduced to 24 mesh crumbs ismixed with 0.5 part of tertiary lauryl mercaptan, 1.5 parts of- Houdrynaphtha, 1.5 parts of lecithin, and 1.5 parts of water, and passedthrough the screw plasticator with a reaction period of about 2.8minutes at a temperature of about 370 F. There is obtained an excellentreclaim having a Williams plasticity number of 4.25.

Example XI 95 parts of 30 mesh red inner tube stock is mixed with 5.84parts of tertiary dodecyl mercaptan and subjected for 1 hour to atemperature of 338 F. in an open steam pan in an autoclave. There isobtained a very satisfactory soft reclaim having a Williams plasticitynumber of 3.27.

Example XII 95 parts of 30 mesh red inner tube stock were mixed with4.73 parts of tertiary decyl mercaptan and devulcanized in pans in opensteam at 338 F. for 1 hour in an autoclave. A very soft and tackyreclaim was obtained.

Epample XIII 95 parts of red inner tube scrap in crumb form of 12 meshsize are mixed with a solution consisting of 3.5 parts of Solvesso #3, 1part of engine oil, and 2 parts of di-tertiary-butyl disulflde, theresulting mixture is passed through a tubing machine provided with anozzle for an annular opening a few millimeters in radius and 95 partsof natura1 rubber peels reduced to 24 mesh crumbs is mixed with 0.5 partof di-tertiary hexyl disulfide, 1.5 parts of Houdry naphtha, 1.5 partsof engine oil, 0.5 part of lecithin, and 1.5 parts of water and passedthrough the screw plasticator with a reaction period of about 2.8minutes at a temperature of about 378 F. having a Williams plasticitynumber of 3.88.

Example XV 4'7 .5 parts of 12 mesh Buna S peels are blended with 47.5parts by weight of 12 mesh natural rubber peels and thoroughly mixedwith 1 part di-tertiary-butyl disulfide, 1.5 parts Solvesso #3, 0.5 partlecithin, and 1.5 parts of water. This stock is then passed through a 3"diameter screw plasticator equipped with a 2%? pin in a 3" die, rotatingat 70 R. P. M. at a temperature of 355-382 F. and a rate of 26.8 lbs.per hour. The

resulting product is an excellent reclaim of 5.16 Williams plasticityand a tensile strength of 1108 lbs. when compounded by the ReclaimAssociation formula at 40 lbs. steam for 30 minutes.

Example XVI 95.0 parts of Buna S peels are mixed with 1.5 partsdi-tertiary-butyl disulfide, 1.50 parts Solvesso #3, 0.25 parts oleicacid, 5.00 parts Naftolen R-100, 1.50 parts di-secondary-butyl catechol,and 1.50 parts or water. This mixture is then processed through a 3"diameter plasticator rotating at 104 R. P. M. equipped with a 15%" pinin a 2" diameter die at 340-862 F. at a rate of 26 lbs per hour. Theproduct is a good reclaim of 5.45 Williams plasticity.

Example XVII 95.0 parts of 30 mesh red inner tube scrap were heated with5.00 parts of di-tertiary-butyl disulfide for one hour in pans in opensteam at 338 F. The product was a satisfactory reclaim of Williamsplasticity number 4.57. Certain subject matter disclosed but not claimedherein is claimed in the following applications, filed by me and EdwardF. Sverdrup; Serial No. 695,630, filed September 9. 1946; Serial No.193,688. filed November 2, 1950; and Serial No. 203,257, filed December29, 1950.

I claim:

1. A method of reclaiming vulcanized rubber which comprises heating suchmaterial to a temperature not substantially less than 300 F. and belowthe temperature of thermal decomposition of the rubber in the presenceof not over 15% of an organic sulfur-containing compound of the classconsisting of aliphatic mercaptans, and aliphatic disulfides in which acarbon to which sulfur is directly attached has three carbon atomsattached thereto.

2. A method of reclaiming material of the class consisting of naturalrubber, polychloroprene, and copolymers of butadiene with styrene oracrylonitrile which comprises heating such material to a temperature notsubstantially less than 300 F. and below the temperature of thermaldecomposition of the material in the presence of not over 15% of analiphatic tertiary mercaptan.

3. A method such as set forth in claim 2 wherein the mercaptan istertiary dodecyl mercaptan.

4. A method of reclaiming vulcanized natural rubber which comprisesheating the rubber to a temperature of from about 300 F. to about 450 F.in the presence of a proportion in the range 0.1 through 7 of thevulcanized rubber by weight of an aliphatic tertiary dodecyl mercaptan.

5. A method of reclaiming material of the class consisting of naturalrubber, polychloroprene, and copolymers of butadiene with styrene oracrylonitrile which comprises heating such material to a temperature notsubstantially less than 300 F. and below the temperature of thermal 7position'of'the material in the presence of not over 15% of an aliphaticdi-tertiary disulfide.

7. A method of reclaiming vulcanized rubber which comprises heating suchvulcanized rubber to atemperature not substantially less than 300 F. andbelow the temperature of thermal decomposition of the'rubber in thepresence of a proportion in the range 0.1 through 7% by weight of thevulcanized rubber of an aliphatic di-tertiary' butyl disulfide.

. '8. A method of devulcanizing natural rubber which comprises heatingsuch rubber to a temperature in the range 300-420 F. in the presence ofnot over 15% of an organic compound of the class consisting of aliphaticdisulfides and aliphati'c'mercaptans in which the carbon of the 5-0group has three other carbon atoms directly attached thereto;

9. A method of reclaiming material of the class consisting of naturalrubber, polychloroprene, and copolymers of butadiene with styrene oracrylonitrile which comprisesheating such material to a temperature notsubstantially less than 300 F. and below the temperature of thermaldecompositionof the material in the presence of a proportion in therange 0.1 through 7 per cent of saidvulcanized material by weight of anorganic compound of the class consisting of aliphatic disulfides, andaliphatic mercaptans in which the carbon of the'S--C group has threeother carbon atoms directly attached thereto.

10. A method of reclaiming material of the class consisting of naturalrubber, polychloroprene, and copolymers of butadiene with styrene oracrylonitrile which comprises heating such material to a temperature inthe range 300-420 F. in the presence of a proportion in the range 0.1through '7 per cent of the vulcanized material by weight of an organicsulfur-containing compound of the class consisting of aliphaticmercaptans and aliphatic disulfides in which a carbon to which sulfur isdirectly attached has three carbon atoms attached thereto. 7

JOSEPH C. ELGIN.

REFERENCES CITED The following references are of record'in the file ofthis patent;

UNITED STATES PATENTS Frolich June 6, 1950

1. A METHOD OF RECLAIMING VULCANIZED RUBBER WHICH COMPRISES HEATING SUCHMATERIAL TO A TEMPERATURE NOT SUBSTANTIALLY LESS THAN 300* F. AND BELOWTHE TEMPERATURE OF THERMAL DECOMPOSITION OF THE RUBBER IN THE PRESENCEOF NOT OVER 15% OF AN ORGANIC SULFUR-CONTAINING COMPOUND OF THE CLASSCONSISTING OF ALIPHATIC MERCAPTANS, AND ALIPHATIC DISULFIDES IN WHICH ACARBON TO WHICH SULFUR IS DIRECTLY ATTACHED HAS THREE CARBON ATOMSATTACHED THERETO.